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deserve personal mention. Very special thanks are due to Professor Alistair Cochran, one of the pioneers of the sentinel lymph node technique at UCLA, for encouraging comments and extremely helpful discussions.

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BACKGROUND The sentinel lymph nodes (SLNs) as the primary targets for lymphatic metastases can be removed selectively by γ probe‐guided sentinel lymph nodectomy (SLNE) in nearly all patients with cutaneous melanoma. Correspondingly high standards in terms of specificity, sensitivity, and microstaging are required for the evaluation of SLNs. METHODS Since 1995, the authors have performed SLNE in 389 lymph node regions (LNRs) on 342 patients with melanoma. The harvested 636 SLNs and a further 1394 nonsentinel lymph nodes (non‐SLNs) were evaluated by standardized, semiserial section histology, including immunohistochemistry. For each LNR, this technique permitted routine S classification using two simple morphometric parameters: the number of tumor‐involved, 1‐mm slices of the SLNs (n) and the centripetal depth of metastatic cell invasion (d). S1 was defined by 1 ≤ n ≤ 2 and d ≤ 1 mm, equivalent to localized peripheral tumor cell deposits; S2 was defined by n > 2 and d ≤ 1 mm, indicating more extended peripheral metastases; S3 was defined by d > 1 mm in SNLs with deeper metastatic infiltration; and S0 meant no detectable tumor cells (n = 0). RESULTS The authors diagnosed 325 SLNs as S0, 24 SLNs as S1, 22 SLNs as S2, and 18 SLNs as S3. The occurrence of at least one melanoma‐positive non‐SLN subsequent regional completion lymph node dissection (RCLND) significantly increased from 0 of 12 in S1 SLNs to 2 of 13 in S2 SLNs and 9 of 15 in S3 SLNs (P = 0.001; chi‐square test). Like the T classification of the primary melanoma, the S classification proved to be a highly significant predictor for distant metastasis (P < 0.001). It turned out to be an independent factor of influence on distant metastasis and survival in multivariate Cox analyses, which included tumor thickness, primary tumor site, patient gender, and patient age as covariates. CONCLUSIONS The data presented recommend the S‐staging concept as a promising option to fill a gap between the T and conventional N component of the pTNM classification. If its predictive capacity can be confirmed in multicenter studies, then the S classification may become the decisive criterion for or against RCLND, and a combined T plus S staging system will help to improve prognostically relevant stratification of melanoma patients in adjuvant therapy trials. Cancer 2001;91:2110–20. © 2001 American Cancer Society.

gamma-Probe-guided SLNE is a reliable procedure with minimal complications that should be performed in all pT3 + 4 (intraoperative frozen section histology) melanomas without clinically evident metastases.